Method for constructing transportation pipes and heat generating pipes utilizing skin-effect current

ABSTRACT

Units of transportation pipes heated by the skin-effect current flowing concentratedly only through the inner wall skin portion of a ferromagnetic pipe in which an insulated conductor line forming a primary circuit is placed to pass AC therethrough are constructed by electrically connecting the skin-effect current heat-generating pipes at all connecting parts of the transportation pipe so as to form a secondary circuit in all units of the transportation pipe by an electric connection between the said unit of the transportation pipe and the corresponding part of the skin-effect current heat-generating pipe.

United States Patent Ando 51 May 23, 1972 [54] METHOD FOR CONSTRUCTINGTRANSPORTATION PIPES AND HEAT GENERATING PIPES UTILIZING SKIN- EFFECTCURRENT [72] Inventor: Masao Ando, Yokohama, Japan [73] Assignee: ChissoCorporation, Osaka, Japan [22] "Filed: Mar. 5, 1970 21 Appl. No.: 16,788

3 01 Foreign Application Priority Data Mar. 26, 1969 Japan ..44/229 7452] us. on ..219/301 51 1111.131. ..1-l05b 3/40 581 Field of Search.......219 /300, 301

[56] References Cited UNITED STATES PATENTS 1,273,666 7/1918 Powers..219/301 ux 3,293,407 12/1966 Ando ..219/301 4/1968 Rolfes ..219/300Primary ExaminerR. F. Staubly Att0rney-F red C. Philpitt ABSTRACT Unitsof transportation pipes heated by the skin-effect current flowingconcentratedly only through the inner wall skin portion of aferromagnetic pipe in which an insulated conductor line forming aprimary circuit is placed to pass AC therethrough are constructed byelectrically connecting the skin-effect current heat-generating pipes atall connecting parts of the transportation pipe so as to form asecondary circuit in all units of the transportation pipe by an electricconnection between the said unit of the transportation pipe and thecorresponding part of the skin-effect current heat-generatmg pipe.

5 Claims, 7 Drawing Figures Patented May 23, 1972 3,665,154

2 Sheets-Sheet 1 FIG. I

FIG. 2

Patented May 23, 1972 2 Sheets-Shut 2 FIG. 4

H FIG.5

METHOD FOR CONSTRUCTING TRANSPORTATION PIPES AND HEAT GENERATING PIPESUTILIZING SKIN- EFFECT CURRENT BACKGROUND OF THE INVENTION Thisinvention relates to a method for constructing liquid transport pipesheated by the skin-effect current appearing in attached heat-generatingpipes made of highly ferromagnetic metal.

The principle of the heat-generating pipe which utilizes the skin-effectcurrent applied in the method of the present invention will be explainedby referring to FIGS. 1 to 3.

In FIG. 1, 1 is a heat-generating pipe having a strong magnetic propertysuch as a steel pipe, 2 is an insulated conductor line passed throughthe steel pipe, one end of which is connected to one terminal of anelectric source and the other end of which is farther from the electricsource and connected to the end of the steel pipe which is farther fromthe electric source. A conductor line 4 connects the remaining other endof the electric source to the other end of the steel pipe which isnearer to the electric source to form an electric circuit.

In such a circuit, let a resistivity of the steel pipe be d (flcm), apermeability be p., frequency be f (Hz), S(cm) which is called a depthof skin is expressed by a formula If there are relations expressed byformulas t 2S, d S, 1 d 2) between S(cm), thickness t(cm), length 1(cm),and inside diameter d(cm) of the steel pipe, alternating currentflowsconcentratedly only through the neighborhood of the inside surface ofthe steel pipe and no potential appears on the outside surface thereof.In other words, even whentwo points of the outside surface of the steelpipe are shorted with a low impedance conductor, no electric currentflows therethrough.

There is an invention which utilizes the above-mentioned phenomenon; forexample, U.S. Pat. No. 3,293,407 entitled Apparatus for MaintainingLiquid being Transported in a Pipeline at an Elevated Temperature.

FIG. 2 shows a case where an electric source is of single phase and twoheat-generating pipes are used.

FIG. 3 is a case where an electric source is of three phases and threeheat-generating pipes are used. The circuits of FIGS. 2 and 3 are thefundamental circuits utilized in the present invention. According to thetransportation pipe to which a heat-generating pipe is attached, two ormore single phase circuits such as that of FIG. 2, i.e., even numberssuch as 4, 6 and 8 of heat-generating pipes; two or more three phasecircuits such as that of FIG. 3, i.e., a multiple of 3, such as 3, 6 and9, of heat-generating pipes are used.

In FIG. 2, 1 and l are heat-generating pipes having strong magneticproperty e.g., steel pipe, and 2 and 2 are insulated conductor linespassed through the steel pipes. One circuit is formed by an electricsource 3, a conductor line 2, a short-circuit line 7 which connects thesteel pipes l and 1', a connecting line 5, the heat-generating pipe 1,another short-circuit line 6 and a connecting line 4. Another circuit islikewise formed by an electric source 3', a conductor line 2, ashortcircuit line 7, a connecting line 5, the heat-generating pipe 1,another short-circuit line 6 and a connecting line 4. If two circuitsare equivalent, it is possible to omit connecting lines 4 and 5 or 4 andmake the electric sources 3 and 3 into one source. Of course in thisinstance the short-circuit lines 6 and 7 remain connected and form asecondary circuit relative to the electric source.

In FIG. 3, l, 1 and 1" are heat-generating pipes having strong magneticproperty, e.g., steel pipes, and 2, 2' and 2" are conductor lines passedthrough these steel pipes. A circuit is formed by an electric source 3,a conductor line 2, short-circuit line 7 which connects the steel pipes1 and 1 wherein the conductor lines 2 and 2' are passed, a connectingline 5, another short-circuit line 6 which connects the steel pipes land 1 wherein the conductor lines 2 and 2' are passed and a connectingline 4. Similarly, respective circuits are formed with regard toelectric sources 3 and 3". If each phase is electrically balanced withthe phases as in FIG. 2, either or both of connecting lines 4 and 5 canbe omitted. Of course in this case of FIG. 3, short-circuit lines 6, 7,6', 7 etc., remain as in FIG. 2 and form a three-phase secondary circuitrelative to the electric source. According to the study of the presentinventor, if the respective circuits of heat-generating pipes areelectrically balanced with each other in FIGS. 2 and 3, either or bothof the connecting lines 4, 5 can be omitted; therefore, the method ofthe present invention utilizes this fact to provide the readiness offabrication in constructing an apparatus of long transportation pipeheated by skin-effect current. Namely when a transportation pipe islong, unit transportation pipes of a unit length having a plurarity ofsuitable heat-generating pipes of skin-effect current which are madeconvenient for its transportation and construction, are constructed onthe spot. In such a case, it is often desirable to avoid use of aheatgenerating steel pipe which is electrically connected so perfectlyas shown in FIGS. 1 to 3, because the fitting of heatgenerating pipes onthe spot by way of, e.g., welding or the like is difficult or even whenthe fitting is possible, fabrication cost, safety and the like oftenprevent its use.

As above-mentioned, in the method of the present invention, such anarrangement is made that a part of the secondary circuit is formed inevery unit heat-generating pipe relative to the primary current flowingthrough the conductor line passing through the inside of theheat-generating pipe.

The above-mentioned arrangement will be illustrated referring to FIGS. 4to 7. FIGS. 4 and 5 show single-phase circuits which correspond to FIG.2 of the fundamental drawing and FIG. 6 is a cross-sectional view.

In FIGS. 4 to 6, l and 1' are heat-generating pipes having strongmagnetic property, e.g., steel pipes and are electrically connected to aunit transportation pipe 8, e.g., by way of welding. 2 and 2' areconductor lines passed through the inside of these steel pipes. In thedrawing, an electric source is omitted but these conductor lines form agoand-return circuit relative to the electric source.

In FIG. 4, a unit transportations pipe 8 has flanges- 9 by which theunit transportation pipe 8 is connected to the next one on the spot tocomplete the arrangement. In this instance, since a heat-generating pipe1 is attached, e.g., by welding to the transportation pipe 8 as a unitheat-generating pipe, it is fairly difficult to connect neighboringheat-generating pipes mutually.

In FIG. 4, however, when a unit transportation pipe 8 is an electricconductor such as a steel pipe, each heat-generating pipe is notnecessarily to be connected with each other. Of course, the conductorlines 2 and 2' must be connected as above-mentioned. As shown in FIG. 4,when the heat-generating pipes l and 1 are divided by a flange part 9, asecondary current which flows from the hea t-generating pipes I and 1'into the transportation pipe, further flows into a part 6 7 of thetransportation pipe thereby to form a secondary circuit as in case ofFIG. 2 wherein the heat-generating pipes constitute the secondarycircuit relative to the primary circuit constituted by the conductorlines 2 and 2. Since the part 6 7 of the transportation pipe hasextremely low impedance, this current never flows to the outside of thetransportation pipe. Particularly since the transportation pipe of thiskind is enclosed by a heat-insulating layer 11, there is no danger ofcontact of the metal part with an outside material. Even provided thatthe contact of the metal part should happen, the leakage current betweentwo neighboring heat-generating pipes is only a trifle extent as much asseveral tens milivolt and practically negligible because the distancebetween the two neighboring heat-generating pipes is usually less than 1meter.

FIG. 5 shows a case where neighboring unit transportation pipes 8 arelaid by welding and heat-generating pipes are connected by a connectingbox 10. The method which uses this connecting box can also be used incase of the flange connection as shown in FIG. 4 where unittransportation pipes 8 are connected with a flange 9.

Even when such a connecting box 10 is used, it is often difficult toelectrically connect the connecting box by e.g., welding perfectly.

According to the method of the present invention, even whenheabgenerating pipes are not electrically connected mutually by aspecial way, the heat-generating pipe constitutes a secondary circuitand generates heat as in case of FIG. 4.

Namely in FIG. 5, insulated conductor lines 2 and 2 form a goand-returnprimary circuit relative to an electric source after passed through theinsides of heat-generating pipes 1 and I though the electric source andparts of terminal connection are omitted in the drawing. 9 isa'connecting part of unit transportation pipes. In this case, thewelding of transportation pipe provides a connection which is almostelectrically perfect; hence a part of the secondary circuit formed inthe transportation pipe 8 appears also at such a part as 6 and 7 of FIG.5.

On account of the existence of a connecting box 10 in one part 12 of theheat-generating pipe in which the neighboring parts of theheat-generating pipes I and l and the connecting box 10 are not weldedas shown in FIG. 5, the secondary current which flows through the insidesurface skin of the heatgenerating pipes l and 1' passes the outsideskin of the heatgenerating pipe and appears in one part of thetransportation pipe, i.e., 6 and 7. Accordingly, it should be noted thatin the part 12 of the heat-generating pipe, current flows through boththe inside and the outside surface skins and the amount of heatgeneration is increased there compared with that in other parts of theheat-generating pipe.

In FIG. 4, a case is shown when neighboring flanges 9 are mutuallyelectrically insulated, and in FIG. 5, a case is shown where aconnecting box 10 is made of an insulating material. However, in actualcase, flanges and connecting boxes are, mostly, made of a material suchas steel which allows electric current to flow, hence one part of thesecondary current flows through this part as a separate stream.

In actual transportation pipe facility, distribution of currents inFIGS. 4 and 5 are slightly different but they have nothing to do withthe true nature of the method of the present invention.

FIGS. 6 and 7 are cross-sectional views of the part which are close tothe connecting part of a transportation pipe 8 in which the method ofthe present invention is applied.

FIG. 6 shows a case of single phase where two heat-generating pipes land 1 are used and FIG. 7 shows a case of three phases where threeheat-generating pipes are used. In both the cases, 2 is a conductor linepassed through the inside of a heatgenerating pipe and 6 or 7 is a pathof current.

The foregoing explanation is directed to cases where trans- I portationpipes are constructed with a material having electric conductivity suchas steel, but when unit transportation pipes are constructed with amaterial having electric insulating property such as plastic, it ispossible to connect heat-generating pipes mutually in such a way thatthe impedance of the connecting part is as low as possible by use of amaterial having a good electric conductivity instead of the paths of thecurrent on the surface of the above-mentioned transportation pipe 6, 7,6', 7, etc.

What is claimed is:

1. Apparatus for heating a transportation pipe including a plurality ofdiscontinuous heat-generating pipe sections, a source of electricalenergy, an insulated conductor connected to said source forming aprimary current path, said discontinuous heat-generating pipe sectionsforming series-connected portions of a secondary current path, otherseries-connected portions of said secondary current path being formed ofportions of said transportation pipe.

2. The apparatus of claim 1 wherein said transportation pipe is made ofa metallic material.

3. The apparatus of claim 2 wherein said discontinuous heat-generatingpipe sections are welded to said transportation i e.

4. The apparatus of claim 1 wherein said transportation pipe is made ofnon-metallic material, said plurality of discontinuous heat-generatingpipe sections are attached to said transportation pipe and saiddiscontinuous heat-generating pipe sections are mutually connectedelectrically.

5. A method for constructing units of transportation pipe I heated byskin-effect current flowing through the inner wall skin portion of aferromagnetic pipe including the steps of,

providing said ferromagnetic pipe of a length shorter than said units oftransportation pipe, providing a source of electrical current,

providing a primary circuit path for said current comprising aninsulated conductor passing through said ferromagnetic pipe andconnected to said source,

providing a portion of a secondary path for said current through a wallof said ferromagnetic pipe,

and providing a further secondary path for said current comprising aportion of said units of transportation pipe to form the respectivesecondary circuits in said units of transportation pipe.

1. Apparatus for heating a transportation pipe including a plurality ofdiscontinuous heat-generating pipe sections, a source of electricalenergy, an insulated conductor connected to said source forming aprimary current path, said discontinuous heat-generating pipe sectionsforming series-connected portions of a secondary current path, otherseries-connected portions of said secondary current path being formed ofportions of said transportation pipe.
 2. The apparatus of claim 1wherein said transportation pipe is made of a metallic material.
 3. Theapparatus of claim 2 wherein said discontinuous heat-generating pipesections are welded to said transportation pipe.
 4. The apparatus ofclaim 1 wherein said transportation pipe is made of non-metallicmaterial, said plurality of discontinuous heat-generating pipe sectionsare attached to said transportation pipe and said discontinuousheat-generating pipe sections are mutually connected electrically.
 5. Amethod for constructing units of transportation pipe heated byskin-effect current flowing through the inner wall skin portion of aferromagnetic pipe including the steps of, providing said ferromagneticpipe of a length shorter than said units of transportation pipe,providing a source of electrical current, providing a primary circuitpath for said current comprising an insulated conductor passing throughsaid ferromagnetic pipe and connected to said source, providing aportion of a secondary path for said current through a wall of saidferromagnetic pipe, and providing a further secondary path for saidcurrent comprising a portion of said units of transportation pipe toform the respective secondary circuits in said units of transportationpipe.